A field-effect semiconductor device having a semiconductor body with a main surface is provided. The semiconductor body includes, in a vertical cross-section substantially orthogonal to the main surface, a drift layer of a first conductivity type, a semiconductor mesa of the first conductivity type adjoining the drift layer, substantially extending to the main surface and having two side walls, and two second semiconductor regions of a second conductivity type arranged next to the semiconductor mesa. Each of the two second semiconductor regions forms a pn-junction at least with the drift layer. A rectifying junction is formed at least at one of the two side walls of the mesa. Further, a method for producing a heterojunction semiconductor device is provided.